Document printer having rigidified frame carrying adjustablypositioned,document-advancing tractors



1969 R. J. MORAN ET AL p 3,420,352

DOCUMENT PRINTER HAVING RIGIDIFIED FRAME CARRYING ADJUSTABLY-POSITIONED, DOCUMENT-ADVANGING TRACTORS Filed Oct. 21, 1965 Sheet Of 5 FIG.

INVEN TOR.

ROBERT J.MORAN HAROLD M. SHNEIDER My. Wwi

Jan. 7, 1969 R MORAN ET AL. 3,420,352 DOCUMENT PRINTER HAVING RIGIDIFIED FRAME CARRYING ADJUSTABLY-POSITIONED, DOCUMENT-ADVANCING TRACTORS Filed Oct. 21, 1965 Sheet 2 Of 5 //V VENTO/RS.

Jan. 7, 1969 MORAN ET AL 3,420,352

' DOCUMENT PRINTER HAVING RIGIDIFIED FRAME CARRYING ADJUSTABLY-POSITIONED, DOCUMENT-ADVANCING TRACTORS Filed Oct. 21, 1965 Sheet Of 5 ROBERT J.MORAN HAROLD M- SHNEIDER United States Patent 3,420,352 DOCUMENT PRINTER HAVING RIGID FIED FRAME CARRYING ADJUSTABLE/- POSITIONED, DOCUMENT-ADVANCHNG TRACTORS Robert J. Moran, Littleton, and Harold M. Shneider,

Weston, Mass, assignors to Honeywell lnc., Minneapolis, Minn, a corporation of Delaware Filed Oct. 21, 1965, Ser. No. 499,277 US. Cl. 197133 lnt. Cl. 15415 15/22 3 Claims .m a. M

ABSTRACT OF THE DISCLOSURE The present invention relates to high speed printing apparatus employed in association with data processing systems and particularly to mounting means therein for adjustably supporting printing and paper-feeding elements therein.

High speed printers have proved an extremely valuable output device for computers. However, computers today are. imposing severe constraints upon the structure and operation of printers such as for higher speeds, better accuracy and more reliability. One such constraint demands an extremely accurate positioning of printing and form-feeding elements necessitating that they be mounted from a stable machine frame and yet be quickly and conveniently adjustable in vertical or horizontal positions. For instance, the pairs of tractors which customarily engage the paper forms on which computer output is printed must be quickly and accurately translatable in synchronism relative to the print hammers for horizontal paper positioning. The tractors must also be translatable relative one another for accommodating different form widths as well as for form tensioning, doing such while never deviating from a constant alignment relative to the form plane. This alignment must be maintained over literally miles of form printing and despite the environmental vibration and shock associated with heavy printing machinery. The present invention addresses these problems through an arrangement which suspends tractor blocks on rectangular beams between printer frame sidewalls so as to provide this desired quick adjustability while also stabilizing the support so that the blocks may be translated under perfect control without deviating from exact alignment with the plane of the hammer block. It is thus an object of the invention to mount sheet-feeding means for constant alignment relative to a reference plane and for quick, accurate translation relative to one another. Another object is to so mount form tractors as to stabilize the suspension means therefor as Well as accommodate quick, aligned translations thereof.

To solve the abovementioned problem of supporting and horizontally adjusting tractor pairs, the prior art has provided various structures, all of which are somewhat inadequate. For instance, prior art workers have used tractor-positioning lead-screws as support means on which the weight of the tractor is imposed, leading to an imperfect, binding engagement between tractor blocks and 3,420,352 Patented Jan. 7, 1969 associated lead screws, resulting in a cumbersome, and sometimes inaccurate horizontal positioning action. This design also places a severe strain on the lead screw structure which, ideally comprising a light, thin driving member, is ill-adapted to also serve as a structural support or rigidifying member. Lead screws, being cylindrical and rotatably engaging driven elements, are also poorly adapted to maintain the elements in non-rotating alignment. Other prior art structures have employed a separate cylindrical rod for guiding tractors in alignment during the horizontal positioning thereof. However, such rounded members suffer the rigidifying and alignment inadequacies of the above-mentioned lead-screws. Thus, they are commonly able to guide only a single tractor sprocket wheel, rather than a complete tractor, which may have a pair of such sprocket wheels. The present invention meets the above problems better by employing rigid rectangular support means adapted to conformingly and slidingly engage tractor blocks clamped thereon. This support acts in conjunction With separate lead-screw means for horizontally thrusting tractor block pairs in synchronism without being transversely loaded. More particularly, the invention contemplates linking pairs of such screw rods by crank means for driving upper and lower tractor block pairs in synchronism more efficiently and conveniently. Such an arrangement will be recognized as superior to the common cable-pulley systems employed heretofore to horizontally translate tractor means.

In addition to the above-indicated support-positioning means, the invention also contemplates providing one of each upper and lower tractor block pairs with individual width-adjustmen means whereby the operator may quickly and conveniently displace left and right tractor block pairs relative to one another by translating a tractor block individually, using the form width itself as a guide. A convenient quick-release spring-operated coupling means is provided for this purpose. This coupling also provides horizontal form-tensioning means for controllably separating block pairs. Thus, it is an object of the invention to provide such improved tractor mounting means in association with separate horizontal positioning means for spacing each pair of tractors. Another object is to include means for translating both tractor pairs in synchronism. Yet another object is to provide such apparatus with form-width adjusting tractor separation means allowing operators to simply locate tractors by displacing one from the other according to indicia on a paper form. Another object is to provide quick-release means for such Width-adjustment which is also adapted for form-tensioning adjustments.

Related to the above-indicated problem of mounting tractors is the problem of supporting print hammers to be stably located in close proximity to said tractor means, and the forms driven thereby, while being nonetheless position-adjustable. Prior art arrangements which keep print hammers compactly arrayed and readily accessible for adjustable spacing, alignment and leveling relative to the paper forms are commonly unstable and vibration sensitive. To remedy this, the invention provides a stable, rigid frame for suspending hammers. This arrangement requires only a few easily-fabricated, simple components, also maintaining them accessible for easy maintenance. More particularly, the invention prescribes a hammer mount means employing a simplified plate suspension hung from sidewalls rigidified by the above-mentioned tractor mounting means and suspended so as to minimize misalignment of the hammer block during height adjustments. The arrangement also provides leveling and positioning adjustment means. Thus, it is another object of the invention to provide such an improved tractor mounting arrangement in conjunction with an improved hammer mounting arrangement suspended from common frame portions in stable, aligned relation during positioning adjustments in either arrangement.

Yet another object is to provide such a hammer suspending arrangement using a few simple parts, while providing relatively unidirectional height-adjusting means as well as leveling and lateral positioning means.

The foregoing objects and novel features of the invention are provided in a preferred embodiment of the invention described below which may be characterized as comprising an improved mounting arrangement for printing components comprising airs of tractor blocks arranged to advance forms controllably along a reference plane; a pair of rectangular support means mounted between a pair of sidewall frame portions for stabilization of the latter and sliding engagement with tractor block pairs; print hammer plate means suspended from the sidewall portions for relatively unidirectional translation normal to the reference plane and including a lever-operated form-thickness adjustment means; each pair of tractor blocks being threadably engaged with an associated horizontal positioning means, both horizontal positioning means being rotatable in synchronism by a crank means, and one each of said tractor block pairs having resilientlydetachable engagement and separation means.

The aforegoing and other characteristic object and features of novelty are pointed out with particularity in the claims annexed hereto and forming a part of the present specification. For a better understanding of the in vention, its advantages and specific objects attained with its use, reference should be had to the accompanying drawing and description, wherein there is illustrated and described a preferred embodiment of the invention.

Referring to the drawing, wherein like reference numerals denote like elements:

FIGURE 1 is a side perspective view of a preferred embodiment of the invention as employed for mounting form-feeding and print-hammer sub-assemblies in a highspeed printer;

FIGURE 2 is a plan view of the arrangement in FIG- URE 1, the drive means associated with the print roll and paper engine being additionally indicated;

FIGURE 3 is a schematic side elevation in partial section of the arrangement in FIGURE 1 with many parts omitted for clarity, the section taken along line III-III in FIGURE 2; and

FIGURE 4 is a fragmentary schematic perspective of one of the hammer block alignment stop means indicated in FIGURE 2.

General organization FIGURES 1-3 show a preferred embodiment of the invention in the form of a form-feeding, hammer-mounting portion 1 of a high-speed printer, such as is employed to provide printed output from data processing systems.

Functionally, this embodiment represents an arrangement for transporting a paper web, or form, (not shown), indicated schematically by the dashed line plane PP (FIG- URE 3) past an array of print hammers confronting a print roll PR for selective impacting thereon. Thus, the form is drawn along plane PP by upper and lower form advance means, namely by a pair of upper left and right tractor blocks 31-L, 31-R, respectively and by a pair of lower left and right tractor blocks 41-L, 41-R respectively, as best shown in FIGURES 1 and 2. It will be evident to those skilled in the art that (as schematically indicated in FIGURE 3 with tractor blocks 31-R, 41-R) the upper and lower tractor blocks are adapted and controlled to advance the paper along plane PP in a prescribed manner so as to present prescribed printing lines to the print position established by the type-bearing print roll PR and the array of hammers in hammer block l-l. As is common in the art, hammer block H will be understood to comprise an aligned array of parallel coplanar hammers affixed upon a hammer base 25 and arranged 4 to be positionable in three dimensions relative to print roll PR and the form plane PP.

It will be generally evident that the present embodient provides an improved combination mounting/positioning arrangement for mounting a form advancing means 9 and a hammer block H to be both stably suspended in a prescribed manner between a pair of parallel sidewall portions 7, 7 of the printer frame and to be positionadjustable. Sidewalls 7, 7' are thus spaced apart and rigidly connected by a pair of angular support means, i.e. upper and lower rectangular beams 6, 6, preferably arranged to be parallel and aligned along a prescribed plane, parallel to form-plane PP. Form-advancing arrangement 9 comprises an upper and lower form-advancing means 3, 4 respectively including pairs of tractor blocks 31, 41, respectively, described more particularly below. It will be apparent that upper and lower advancing means 3, 4 respectively are functionally interrelated in that their paper-advancing sprockets may be synchronously rotated by a pair of upper and lower drive shafts 33, 43. Tractor blocks 31, 41 are also arranged to be horizontally positionable in synchronism by a horizontal positioning means 5 (FIGURE 1) comprising a crank 53, adapted to rotate a pair of upper and lower leadscrews 35, 45 respectively in synchronism, being attached thereto through a pair of sprockets 57, 57 drivingly coupled through drive chain 51 and idler sprocket 55, as more particularly indicated below. It will be seen that the four tractor blocks (31, 41) of the form-advancing means 9 are arranged to be slideably mounted on the drive shafts so that one pair thereof is carried by each one of the rectangular beams 6, 6, being clamped conformingly thereon. More particularly, form-advancing means 9 includes an upper pair of left and right tractor blocks 31-L, 31R respectively, having the base, or clamp, portions thereof, 37-L, 37-R respectively clamped to conform about the periphery of upper oblong beam 6 so as to be slideably positionable along the longitudinal axis thereof. Each tractor block 31 has a coupling 34 engaged to be driven by upper lead-screw 35 for the simultaneous horizontal positioning of the tractor blocks along the longitudinal axis of beam 6. Further, the coupling 34 on tractor block 31R is detaehably engaged with lead screw 35 by means of a quick-release mechanism (described in further detail hereinbelow) to enable the tractor block to be positioned manually along the lead screw 35 for adjusting the spacing relative to its counterpart tractor block 31L. A driven sprocket 32 on each tractor block 31 is engaged to be driven by a splined upper drive shaft 33, this driven sprocket 32' being coupled to an idler sprocket 32 by a drive belt (not shown) for synchronous rotation of the sprocket pair 3232' as is conventional in the art.

In a similar manner, lower form-advance means 4 comprises a pair of tractor blocks 41-L, 41R, slideably mounted through the base portions 47-L, 47-R thereof on lower oblong beam 6', being clamped conformingly thereon. Blocks 41 are adapted to be horizontally translated by lower lead-screw 45, the sprocket pairs thereof being synchronously rotatable, one being engaged to be driven by lower splined drive shaft 43 and the other belt-coupled therewith.

In addition to the above-indicated form advancement arrangement 9, the rigidified frame arrangement provided by sidewalls 7, 7' interconnected by rectangular beams 6, 6' provides a stable mount for a hammer suspension 2. However, suspension 2 functionally comprises a base plate 21, adapted to be suspended from sidewalls 7, 7 by a pair of arcuate hangers 23, 23 which are pivotably journaled therein through a pair of axles 24, 24' respectively. Base plate 21 is thus pivotable about axles 24, 24 for the free suspension thereof. Axles 24, 24 are centered along the paper plane PP as explained below. Base plate 21 is maintained between prescribed limits of depending suspension by a supporting roller cam means 29' being gravity-urged thereagainst. Cam 29' is eccentrically mounted on a rotatable shaft 29 and adapted to be manually rotatable by a lever L, to different angular positions, indicated by a gauge G and corresponding to different hammer spacing distances from form-plane P-P. Lever L thus provides a form-thickness adjustability. As indicated in FIGURE 3, the mounting base 25 for hammer block H is supported by depending base plate 21, being adjustably located thereon by a pair of corner stop means 27, 27', the dependence of base plate 21 being maintained so that base 25 is always gravity-urged against stops 27, 27'. Base 25 is adapted to be adjustably positioned above the surface of plate 21, being supported thereon by a tripod leveling arrangement comprising a set of three leveling bolts B, B, B", being secured thereto by a set of three securing screws 22, one being associated with each of bolts B, B, B". A pair of positioning front set screws 28-1 28'F are provided at the front of stops 27, 27', respectively; a similar pair of side screws 28-8, 28'S being provided at corner stops 27, 27' for aligning the lateral position of hammer base 25 in the plane of plate 21. It will thus be apparent that hammer suspension 2 is adapted to provide a simple mounting means for hammer block H which is adjustable in position so as to be adjustably spaced from print roll PR and so as to be laterally alignable therewith as well as to be levelable so that the type font is parallel with print roll PR. It will be apparent to those skilled in the art that such adjustments are commonly necessary. For instance, the leveling is necessary to compensate for any misalignment between the suspension of print roll PR and that of hammer mount 2 and block H thereon. Print roll-hammer spacing is commonly adjusted to allow for different form-thickness (different number of car-hon copies, for example); while lateral hammer alignment is provided to compensate for any skew between type rows along roll PR and the hammers aligned along hammer block H. Thus, hammer-aligning set screws 28F, 28-S, 28-F, 28'4 will be seen to align the hammer block horizontally and vertically (in plane of base 21) with respect to print roll PR.

Form positioning The paper advance assembly 9 comprising upper and lower advance means 3, 4 respectively will now be particularly described, referring to FIGURES l and 2 especially. Upper drive means 3 comprises left and right upper tractor blocks 31-L, 31-R respectively mounted slidingly on oblong support beam 6 and operatively associated both with upper (horizontal-positioning) lead screw 35 and with upper splined drive shaft 33. Lower drive means 4 similarly comprises left and right lower tractor blocks 41-L, 41-R, respectively, mounted slidingly on oblong support beam 6' and operatively associated with lower lead screw 45 and with lower splined drive shaft 43.

Drive shafts 3-3, 43 extend between sidewalls 7, 7', being rotatably journaled therein; the ends of shafts 33, 43 which extend through one sidewall 7' being coupled to drive pulleys 65, 61, respectively. Shafts 33, 43 are adapted to be rotated in synclironism by a drive motor M having a control means C (FIGURE 2) adapted to controllably rotate a main drive pulley 63 which, in turn, synchronously rotates pulleys 65, 61, being drivingly connected thereto through a timing belt means (not shown) as is conventional in the art. Upper and lower lead screws 35, 45 are journaled in one sidewall 7 and project therebeyond to engage drive sprocket means 57, 57' respectively. As shown in FIGURE 2, the illustrated lead screws 35, 45 do not extend the full distance to sidewall 7' and hence do not engage that sidewall. Tractor blocks 31, 41 are, in the main, relatively conventional, each including a pair of driven and idler sprockets 32', 32 and 42', 42 respectively, each pair being arranged to be rotatably driven by one of the splined drive shafts (33, 43) engaged with the driving sprocket (32, 42'), a

sprocket chain interconnecting the sprocket pairs, as is known in the art. The spline on drive shafts 33, 43 is conventional and permits longitudinal translation of a sprocket relative to the shaft without disengagement. Thus, drive motor M and the above-described connecting drive linkage is adapted to incrementally and periodically rotate the tractor sprocket pairs to periodically synchronously advance lines of paper evenly, at prescribed controlled times. Tractor blocks 41, 31 thus comprise body portions 46, 36 respectively journaling the above-mentioned pairs of sprockets 42, 42' and 32, 32, respectively. Body portions 36, 46 are fixedly mounted on hollow base clamps 37-L, 37-R, 47-L, 47-R which are internally bored to slideably engage the peripheral guide surfaces 6a, 6a (FIGURE 3) of rectangular beams 6', 6. Base clamps 37-L, 37-R, 47-L, 47R thus maintain the alignment of blocks 41, 31 respectively and of the paperengaging pins of sprockets 42, 42', 32, 32' carried thereby. The pins are thus kept aligned to be presented to drive paper forms along plane P-P. While base clamps 37-L, 37-R, 47-L, 47-R may be formed in a number of ways, it has been found convenient to cut out channel portions conforming to the periphery of the associated beam 6 or 6 on three sides thereof leaving the bottom, or fourth, side open and adapted to be closed by clamp sections 39, 49 (FIGURE 3) respectively, for convenience of attachment. Thus mounted, it will be apparent that tractor blocks 31, 41 will be maintained in prescribed parallel angular alignment relative to the longitudinal axes of support beams .6, 6' and yet be easily translated therealong, such as by the rotation of lead screws 35, 45 and, in addition manually in the case of blocks 31R, 41-R. It is thus a feature of the invention that the formadvancing tractor blocks may be slideably mounted between frame sidewalls upon angular support beam means extending therebetween to provide a rigid, stable, wallstabilizin'g tractor mounting structure. This structure can better carry the bulk of the tractor weight, while facilitating translation adjustments thereof and assisting the operation both of the positioning screws and of the sprocket-driving shafts by keeping them unloaded and aligned. Thus, the present beam structure in the printer frame corrects the above-noted prior art problems of straining and binding of tractor-positioning lead screws, and also of tractor-operating drive shafts by essentially eliminating the binding stresses exerted on these screws and shafts by the tractors.

It is another feature of the invention that this horizontal translation of tractor block pairs 31, 41 may be accomplished by the operator using a convenient crank assembly 5. Thus, by the rotation of crank 53, an operator can rotate lower sprocket 57 attached drivingly to lead-screw 45 and, through the coupling of drive chain 51, synchronously rotate upper sprocket 57 and leadscrew 35, attached thereto. A tension-maintaining idler sprocket 55 is provided for improving cranking efficiency and adjusting chain tension. With this indicated horizontal positioning (lead-screw) arrangement, it is apparent that both pairs of tractor blocks 31, 4.1 may be synchronously and uni-directionally translated laterally for horizontal positioning convenience, while being kept aligned.

According to another feature of the invention, tractorspacing, i.e. the separation distance between pairs of tractor blocks 31, 41, is quickly and accurately adjustable. Thus, the couplings 34, 44 on tractor blocks 31-R, 41-R respectively are arranged to be manually manipulated, illustratively depressed, to disengage the coupling from the associated lead screw thereby allowing manual movement of the associated tractor block along the lead screw. Thus, when a form is inserted over the tractor pairs and the sprocket holes on one side of one form are engaged with the tractors on one side (for example, engaged with the sprocket pins on left hand tractor blocks 31-L, 41-L), the companion blocks (e.g. blocks 31-R, 41R) may be horizontally displaced to follow the exact width of this form being released at couplings 34, 44 and moved to register with the opposite (e.g. right hand) sprocket holes of the form. As best seen in FIG- URES l and 3, couplings 34, 44 are made resiliently detachable to disengage the associated tractor blocks 31-R, 41-R, respectively, from their associated leadscrews 35, 45. It is preferred to employ the structure of the type indicated in FIGURE 3 wherein couplings 34, 44 comprise collar portions 44.1, 341 rotatably clamped to blocks 46, 36. Collars 441, 341 are centrally bored to receive associated lead-screw 45, 35 and have a recess extending thereinto from one (top) side thereof to accommodate sprung half-nuts 443, 343, including spring bias means to urge the threaded portion of nuts 443, 343 (upward) normally into engagement with associated leadscrews 45, 35. It will be apparent that an operator may depress half-nut 443 (or 343) to disengage block 41-R (or 31-R) from associated lead-screw 45 (or 35) to laterally shift it and change its spacing from companion lower block 41-L, or (31-L), doing so quickly and accurately. This spacing adjustment (for form-width) may be made using the sprocket holes along forms themselves for a guide. A fine (Vernier) spacing adjustment (be tween pairs of tractor blocks 31, 41) may be made by rotating collars 441, 341 with nuts 443, 343 engaged with lead screws 45, 35 respectively. This operation may also provide horizontal tensioning f the form.

It will be apparent that the above-indicated tractorspacing/positioning-adjust arrangement of the invention provides an improved upper and lower document advancing means 3, 4 capable of providing accurate horizontal positioning of tractor block pairs, both together, for form-positioning and separately for form-spacing; that these tractor block pairs are mounted at a prescribed common attitude along rigid angular support beam structures, extending between frame members so as to support the tractor blocks for sliding translation therealong and so as to relieve the drive shaft and positioning shaft means associated with these blocks.

Hammer suspension The improved hammer plate mounting means above referred to and functionally characterized as hammer suspension 2 has already been generally indicated. A feature of the invention is that the invention provides a hammer block-supporting base plate 21 to be suspended in stable, rigid relation with sidewalls 7, 7 being rigidified by the above-mentioned beam members 6, 6 and pivotably positioned so as to assume a constant prescribed attitude relative to printing plane (or paper path) P-P and to be position-adjustable relatively normal thereto for form-thickness adjustments. Base plate 21 is pivotably suspended by a pair of arcuate brackets 23, 23 rotatably journaled in sidewalls 7, 7' on bracket axles 24, 24' as indicated. Axles 24, 24' are centered along plane P-P preferably so as to pivot the hammers relatively normal to print roll PR, uni-directionally, minimizing off-normal movements. Elevation adjustment means for plate 21 is provided by a roller cam means 29, eccentrically mounted on a cam shaft 29 to be rotated therewith. Lever L is provided to rotate shaft 29 over a prescribed arc sector, in the course of which plate 21 will be raised and lowered, toward or away from, printing plane PP, which is tangent to the operative portion of print roll PR.

Hammer block H is very schematicaly shown since it is of a well-known type, comprising a first hammer mount HM on which are mounted a linear type-slug array HS and associated actuator array including a lever LL arranged to drive alternate slugs and pivot means HP therefor. An adjacent mount HM carries complementary levers LL and pivot means HP.

Hammer block H is mounted on hammer base 25, which, in turn, is supported upon plate 21 by adjustable positioning and leveling means including a tripod array of leveling screws B, B, B". It will be apparent that the relative adjustment of these screws will serve to thrust hammer block H above plate 21 to level hammer slugs relative to print roll PR. A plurality of hold-down screws and associated washers 22 are provided to extend through oversized bores in base 25 and threadably engage plate 21 to maintain this leveled relation and prevent jiggling of hammer block H on plate 21. Screws 22 are disposed in-board of their associated leveling bolts. The operator may adjust the lateral position of hammer plate H into horizontal and vertical alignment with the type on print roll PR by adjusting set screws 28F, 28'F and set screws 28-5, 28S, respectively, for the preferred horrizontal position. A pair of corner stops 27, 27' carrying the above-mentioned set screws 28-F, 28-8, 28-S, 28-F are affixed to the surface of base 21, as indicated, to have their side portions relatively parallel for the engagement of the corners of base plate 25. It will be apparent that, preferably, hammer plate 21 is kept susended so that base 25 may 'be gravity-urged against corner stops 27, 27'. It will be recognized that such an arrangement is a simplified one, dispensing with positioning and coupling means otherwise necessary in, and employed by prior art devices. Those skilled in the art will recognize that the above-described hammer positioning arrangement 2 is openly-accessible such as for maintenace or replacement purposes, etc. The arrangement is easier to fabricate and to adjust, employing only a few parts which are simple and relatively compact, being fitted aptly into print head 1 without overcomplieating it.

Although it is believed that the overall operation of the print head 1, including paper advance means 9 and hammer position means 2, will be evident to those skilled in the art from the above description, for purposes of clarity, it may be summarized as follows. To inject a form into head 1 along plane PP, between print roll PR and the hammers of hammer block H, an operator will uncover the sprockets on the four tractor blocks 31, 41 by swinging print roll PR up away from the print head 1 and unlocking the top guides thereon. The operator then engages the sprocket holes along the left side of the form into the sprocket pins associated with left tractors 31I., 41-L; thereafter, snapping the associated guides back in place. The form-width adjustment may now be made by laterally displacing right tractor blocks 31-R, 41-R through the manipulation of resilient quick-release couplings 34, 44 to disengage the associated lead-screws and slide the tractor blocks 31-R, 41-R along the respective beams 6, 6' until the sprocket pins thereof come into registry with the sprocket holes along the righthand margin of the form. At this point the couplings 34, 44 will be released to re-engage their associated lead-screws, the sprockets on blocks 31-R and 41-R will be drivingly engaged with sprocket holes in the form and the paper guides locked thereon. Next, the operator will adjust the proper horizontal tension by rotatably back-off couplings 34, 44 (collars 341, 441 thereof) the required amount. If it appears neces sary, horizontal centering of the four tractor blocks 31, 41 is performed, the blocks being horizontally translated in unison by rotating crank 53 so as to synchronously rotate lead-screws 35, 45 and thus slidingly thrust the associated block pairs 31, 41 in unison along their respective support beams 6, 6. It will be evident that this provides a quick, convenient centering arrangement to translate the form relative to hammer block H or a particular selected portion thereof.

Form-thickness lever L may now be manipulated for print roll-to-hammer spacing adjustment, determined according to the number of (thickness of) sheets to be printed (number of carbon copies, etc.). This is done by elevating, or depressing, hammer mounting piate 21 by rotating lever L to the appropriate angular position, indicated at gauge G. Lever L will, in the normal case, be maintained at the selected angular position by the frictional forces loading its associated camshaft, as has been observed in practice; however, workers in the art may prefer to provide detent cavities at these positions to receive a sprung-ball detent in a conventional manner for positive indexing. If it appears that the hammers are not aligned along the type-axis of print roll PR, lateral (horizontal and vertical) positioning adjustments may be made at the set screws 28-F, 28-8, 28-F, 28'S in corner stops 27, 27'. Similarly, if the hammers on hammer plate H are not parallel to the surface of the type on print roll PR-;(such as indicated by a variance in contrast across a line of print), a leveling adjustment may be made at leveling bolts B, B, B" after which hold-down screws 22 are tightened. It will thus be apparent that the abovedescribed embodiment provides a simplified, more convenient, improved printing head, especially including means for positioning the paper and hammers relative to one another.

What is claimed is:

1. A document printer having a mechanism for advancing a document into printing alignment with a printing mechanism, said printer having (i) a frame for supporting said advancing mechanism;

and

(ii) motor means for operating said advancing mechanism, and being characterized by the improvement wherein (A) said frame comprises (1) first and second spaced apart, upstanding sidewalls (7, 7') substantially parallel to each other, and

(2) first and second parallel beam members (6, 6') interconnecting said sidewalls to form therewith a rigid solid frame unit, each beam member having at least one selectively oriented substantially flat guide surface (6a, 6'a) along the length thereof, where said guide surface orientation is about an axis parallel to the lengths of said beam members between said sidewalls,

(B) said advancing mechanism comprises (1) a pair of first tractor means (31-R, 31- L) and a pair of second tractor means (41- R, 41-L),

(2) each first tractor means (a) being carried on said first beam member and slideable therealong in said orientation determined by said guide surface on said first beam member,

(b) having a rotatable driven member (32) arranged in said tractor means to cause advancement of a document in said printer when rotated,

(3) each second tractor means (a) being carried on said second beam member and slidable therealong in said orientation determined by said guide surface on said second beam member,

(b) having a rotatable driven member (32') arranged in said tractor means to cause advancement of a document in said printer when rotated,

(C) said motor means (M, 61, 65, 33, 43) is mounted on said frame and engages said driven members of said tractor means to rotate said driven members,

(D) said advancing mechanism further compris- .(1) first and second rotatable lead screws (35, 45) extending parallel to each other along at least part of the span of said beam members between said frame sidewalls and each supported from at least one sidewall for rotation relative thereto,

(2) each first tractor means threadably engaging said first lead screw to be translated along said first beam member in response to rotation of said first lead screw, and

(3) each second tractor means threadably engaging said second lead screw to be translated along said second base member in response to rotation of said second lead screw,

(E) so that each tractor means is carried on and positioned by one beam member, and each lead screw is substantially free of bending stress loading from the tractor means engaged therewith.

2. A printer as defined in claim 1 further characterized in that each lead screw is free of mechanical engagement with the other sidewall.

3. A document printer having a mechanism for advancing a document into printing alignment with a printing mechanism, said printer having (i) a frame for supporting said advancing and printing mechanisms and (ii) motor means for operating said advancing mechanism, and being characterized by the improvement wherein (A) said frame comprises (1) first and second spaced apart, upstanding sidewalls (7, 7) substantially parallel to each other, and

(2) first and second parallel beam members (6, 6) interconnecting said sidewalls to form therewith a rigid solid frame unit, each beam member having at least one selectively oriented substantially flat guide surface (6a, 6'a) along the length thereof, where said guide surface orientation is about an axis parallel to the length of said beam members between said sidewalls,

(B) said motor means is mounted on said frame and includes first and second rotatable drive shafts (33, 43) extending parallel to said first and second beam members and rotatable in synchronism with each other, each shaft being mounted from at least one sidewall for rotation relative to said frame,

(C) said advancing mechanism comprises (1) a pair of first tractor means (31-R, 31-

L) and a pair of tractor means (41-R, 41-L,)

(2) each first tractor means (a) being carried on said first beam member and slidable therealong in said orientation determined by said guide surface on said first beam member,

(b) having a rotatable driven member (32) engaged with said first shaft for sliding therealong and for rotation therewith and arranged in said tractor means to cause advancement of a document in said printer when said motor means rotates said first shaft,

(3) each second tractor means (a) being carried on said second beam member and slidable therealong in said orientation determined by said guide surface on said second beam member,

(b) having a rotatable driven member (32) engaged with said second shaft for sliding therealong and for rotation therewith and arranged in said tractor means to cause advancement of a document in said printer when said motor means rotates said second shaft,

,(D) said advancing mechanism further compris- (1) first and second rotatable lead screws (35, 45) extending parallel to each other along at least part of the span of said beam members between said frame sidewalls and each supported from at least one sidewall for rotation relative thereto,

(2) each first tractor means threadably engaging said first lead screw to be translated along said first beam member in response to rotation of said first lead screw, and

(3) each second tractor means threadably engaging said second lead screw to be translated along said second beam member in response to rotation of said second lead screw,

(E) so that each tractor means is carried on and positioned by one beam member and each lead screw and each drive shaft is free of significant bending stress loading from the tractor means engaged therewith.

References Cited UNITED STATES PATENTS 2,285,197 6/1942 Euth 1'97133 3,114,491 12/1963 Wright 197133 X 3,147,900 9/1964 Konkel 2261 11 3,154,235 10/1964 Hubbard 197133 X 3,155,032 11/1964 Antonucci 10193 X 3,169,473 2/1965 Irwin et al. 101'93 3,200,739 8/1965 Antonucci 101-93 FOREIGN PATENTS 935,129 8/1963 Great Britain.

US. Cl. X.R. 

